Two-storey extensions in the Sevenoaks district follow from two house types. The 1930s and post-war semis of Swanley, Hextable and Dunton Green, often with a garage beside them, take a two-storey side extension over the garage. The large detached and Edwardian houses of Sevenoaks town, Kippington and Wildernesse take a full-width rear extension or a remodel. The council reads both as additions that must stay subordinate, so the gap to the boundary, the roof form and the first-floor windows usually decide the outcome before the depth does, and in the Green Belt the bulk is tested against the original house.
The permitted development rules for two-storey extensions
A two-storey rear extension is permitted development only within tight limits: no more than 3 m deep, at least 7 m from the rear boundary, no higher than the existing house, eaves matching the existing eaves, materials similar in appearance, and any upper-floor side window obscure-glazed and non-opening below 1.7 m.
Most two-storey extensions exceed one of those limits, most often the 7 m rear boundary rule on London plots, so the usual route is a householder planning application. Flats have no permitted development rights.
What changes in Sevenoaks
Extensions of more than one storey are not permitted development in a conservation area, so planning permission is always needed there.
The local constraints that most often decide the route in Sevenoaks are listed below, taken from our Sevenoaks area page. Each one is a reason to confirm the address on Sevenoaks' constraints map before relying on permitted development.
- Green Belt. Most of the Sevenoaks district outside the built-up areas of Sevenoaks town, Swanley, Westerham, Edenbridge and the larger villages is Metropolitan Green Belt. Source
- Kent Downs National Landscape. The Kent Downs National Landscape (formerly the Kent Downs AONB) covers the North Downs across much of the district, including Otford, Kemsing, Shoreham, Westerham and the countryside north of Sevenoaks town. Source
- Conservation areas. Sevenoaks has around 40 conservation areas, including Sevenoaks High Street and The Vine, Westerham, Otford, Kemsing, Shoreham, Edenbridge, Riverhead, Chevening and many smaller village centres. Source
- Knole Park and listed buildings. Knole House and its deer park sit on the edge of Sevenoaks town, and the town, Westerham, Otford, Shoreham, Edenbridge and the villages contain a very high concentration of listed houses, cottages and churches. Source
- River Darent and River Eden flood risk. The River Darent runs from Westerham through Riverhead, Otford and Shoreham, and the River Eden runs through Edenbridge; land alongside both sits in Flood Zones 2 and 3. Source
Gaps, set-backs and roofs on a Sevenoaks street
Sevenoaks' Residential Extensions guidance warns that infilling the spaces between traditional detached and semi-detached houses with two-storey extensions can create a terraced and cramped appearance, and that a side extension flush with the front wall can upset the symmetry of a pair of semis. Where a street has a pattern of gaps, it treats a minimum of 1 metre between the side wall of a two-storey side extension and the boundary, for the full height, as normally desirable, and says the gap may need to be wider depending on context.
It adds that a side extension should not dominate the original building, which it says is helped by reducing the bulk, setting it back from the front elevation and giving it a lower roof. Extension roofs should normally match the main roof pitch, and flat-roofed extensions are unlikely to be permitted unless flat roofs already characterise the locality. On a pitched 1930s house that points to a hipped or pitched first floor, not a flat-roofed box.
Bulk in the Green Belt and windows over the neighbour
In the Green Belt, Policy GB1 requires the extension, taking previous extensions into account, to be proportional and subservient to the original dwelling and not to harm openness through excessive scale, bulk or visual intrusion. The guidance says a large, bulky or intrusive extension is not acceptable, that the test applies even where public views are limited, and that an addition below the 50% floorspace figure can still be disproportionate as a result of design.
On the first floor, the Residential Extensions guidance does not allow windows that would overlook a neighbour's habitable-room windows at close distance or the private area next to the back of their house. It points to oblique positioning, set-backs, high-level windows, and obscure-glazed or non-opening windows as ways to resolve it, and says a side wall facing a neighbour should not normally have windows.
What Sevenoaks planning officers look for
Sevenoaks officers assess householder applications against the Core Strategy 2011, the Allocations and Development Management Plan 2015 and the council's residential extensions guidance, with Green Belt and Kent Downs policy in the background for most of the district. They tend to look for extensions that stay subordinate to the original house in scale and roof form, side extensions set back from the front wall and below the ridge with a gap kept to the boundary, rear extensions that clear the 45-degree line to the neighbour's nearest habitable window, and dormers set back from the eaves and clad in matching tile. In the Green Belt the first question is whether the extension, added to anything built since the house was original, is disproportionate; officers usually measure this by floorspace and volume, and the council's guidance has historically treated additions beyond about half the original as needing a strong case. Common refusal reasons are disproportionate Green Belt additions, side extensions that create a terracing effect, and roof extensions or box dormers in conservation areas.
Fees and timelines
Sevenoaks decides a householder application or a Lawful Development Certificate within 8 weeks of validation. The council fee is £528 for a householder application and £264 for a Lawful Development Certificate (England, from 1 April 2025; verify before applying).
Our own fee is fixed once quoted. The quote tool gives an indicative figure in minutes and a written quote follows within 24 hours.
Primary sources
- Sevenoaks District Council: Residential Extensions SPD (2009)
- Sevenoaks District Council: Development in the Green Belt SPD (2015)
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2: the permitted development limits quoted above.
- Planning Portal: do you need permission: the national guidance and the application service every council accepts.
- Sevenoaks District Council: planning: the council's own constraints map, validation checklist and pre-application service.
